1. Field of the Invention
The present invention relates to a method of generating an interpolation image to improve blurring due to a hold type display device or unnatural movement in a moving image whose frames are few in number, an interpolation image generating apparatus, and an image display system using the same.
2. Description of the Related Art
Generally, there are two kinds of image display devices: an impulse type display device that continues emitting light for only an afterglow time of a fluorescent substance after writing of image (for example, CRT and field emission type display device (FED)), and a hold type display device which continues holding display of a previous frame till an image is newly written (for example, Liquid Crystal Display (LCD), electroluminescence display (ELD), etc.)
A problem of the hold type visual display unit is a blurring phenomenon to produce in displaying a moving image. The blurring phenomenon occurs by the reason that when the eyes of a viewer followed movement of the moving object existing in a moving image consisting of a plurality of frames, the images of the frames are projected on the retina with being superposed. Though the image of a previous frame continues being displayed until the display image is replaced from the previous frame by a next frame, the viewer predicts the image of the next frame and observes the image while moving the eyes on the previous frame in a migration direction of the moving object. In other words, since the eyes have continuous tracking exercise and do sampling with an interval shorter than a frame interval, an image formed by bridging between two adjacent frames is observed as blurring.
This problem can be solved by shortening an interval between display frames. As a result, an unnatural movement of a moving image whose frames are few in number can be improved. It is considered as a concrete technique to form an interpolation image using motion compensation used in MPEG2 (Motion Picture Experts Group phase 2) to interpolate between adjacent frames with the interpolation image. In motion compensation, a motion vector detected by block matching is used. However, since an image is generated in units of a block in MPEG2, when a plurality of objects whose movements differ from one another is included in a block, a part with correlation and a part without correlation appear. The block distortion occurs by the part without correlation.
Japanese Patent Publication (KOKAI) No. 2000-2224593 discloses a frame interpolation method for solving this problem. According to the Publication, in determining a pixel value of a to-be-interpolated block in an interpolation frame, the motion compensated interframe absolute difference value between two frames of a to-be-decoded small block is compared with a threshold every opposite pixels, the block is divided into a first pixel region having an absolute difference value less than a threshold and a second pixel region having an absolute difference value higher than the threshold.
About the first pixel region, an average of the pixel value of the first pixel region and the pixel value of the corresponding pixel in the reference block indicated by a motion vector between two frames is obtained. The average is copied onto the interpolation frame. On the other hand, about the second pixel region, hidden surface relation in a to-be-decoded frame is determined. A motion vector search direction between two frames is again set based on the determination result, and a motion vector is detected. The pixel on the researched reference frame that is indicated by a scaled motion vector is copied onto an interpolation frame. In this way, by means of doing interpolation in units of a pixel region obtained by dividing a to-be-decoded block in two according to the motion compensated interframe absolute difference value between two frames, a block distortion, namely an interpolation error appearing when a plurality of objects whose movements differ from one another are included in the block is reduced.
In the Publication, a search method in the second pixel region performs reshuffling of a frame direction, but an extraction method in a frame to be detected does not touch additional information. It is not appropriated to employ the pixel used in the first pixel region as a pixel of the second pixel region to reflect movement of an actual object. As thus described, to search for the pixels of the second region without doing constrain for the pixels of the first pixel region extracted after region division may cause picture degradation (deterioration for a noise) due to interpolation error.
It is an object of the present invention to provide an interpolation image generating method for doing an intra-frame interpolation without an interpolation error, and an image display system using the same.